Definition

• A localized permanent dilation of the abdominal aorta >3 cm in diameter.

Epidemiology

• Incidence is reported to be 5– 10%.

Aetiology

• Almost all are caused by aortic atherosclerosis.

Pathogenesis

• Proteolytic enzymes weaken the media of the aorta, leading to aneurysmal change. • Increased levels of matrix metalloproteinases have been found in aneurysmal aortas. these enzymes are known to degrade elastin.

Presentation • Unruptured aneurysms are often asymptomatic and most are discovered incidentally on abdominal examination or imaging.

• Ruptured abdominal aortic aneurysms present as a surgical emergency with abdominal pain and shock.

Macroscopy

• the aorta is dilated, usually below the level of the renal arteries.

• extensive atherosclerosis is invariably present, often with secondary thrombosis and calcification.

 Histopathology

 • Aortic atherosclerosis shows intimal collections of lipid, inflammatory cells, and fibrosis. Complicated lesions may show haemorrhage in the plaque or overlying thrombus.

• Aortic aneurysms show severe atherosclerosis with marked loss of the media layer.

 Prognosis

• the natural history is that of gradual enlargement.

 • Risk of rupture is exponentially related to the diameter.

 • Mortality after rupture exceeds 80%.

• elective surgical repair should be considered for aneurysms with a maximum diameter of 5.5 cm or more.